The expression “pipe” as used herein is intended to include pipes and tubes as such, and also pipe-like members and fittings for use in pipework such as bends, elbows, “T” connectors, flange adaptors and parts and devices adapted to be fitted to pipework such as valves and pumps. Such pipes may have a variety offend configurations, and will be plain-ended in contrast to flange-ended.
Pipe coupling devices commonly comprise an annular coupling sleeve that can connect with a plain-ended pipe. The connection can be made via a sealing or gripping member such as a sealing gasket arranged about the plain-ended pipe, and an annular compression member disposed about the end of the sleeve and arranged to be drawn axially against the sealing or gripping member to cause the said member to be forced radially inwardly into sealing contact between the sleeve member and the outer periphery of the plain-ended pipe located within the sleeve. The sleeve and/or the annular compression member are typically provided with radially inclined annular surfaces to assist deformation of the sealing or gripping member in a radially inwards direction.
Such pipe couplings can be formed, for example, of malleable iron, steel or plastics material, the gaskets being formed of an appropriate elastomeric material.
The compression member can be in the form of a compression flange the compression flange being provided with tightening nuts and bolts for connecting together the compression flange with a flange or similar formation on, or associated with, the coupling sleeve. The tightening bolts pass through apertures spaced around the outer extremeties of the respective flanges, such bolts being provided with a head at one end and carrying a nut at the other so that the flanges are drawn together by tightening the nuts and bolts. Alternatively, the compression member may be threaded to enable it to screw into or onto the ends of the sleeve.
One problem confronting manufacturers of pipe couplings is that for pipes having a given nominal outside diameter (O.D.), the pipes in practice may have O.D.s varying over quite a wide range. Thus, couplings need to be capable of being used to connect pipes having a range of O.D.s.
In many known coupling devices, the annular compression member (e.g. compression flange), and the opposing portion of the sleeve against which the sealing or gripping member (e.g. sealing gasket) is compressed, have inclined surfaces, the angles of inclination serving to assist the gasket to be deformed radially inwardly.
In such coupling devices, the sealing or gripping efficiency of the gasket, and/or any gripping element associated therewith is dependent on the input loads exerted as the two inclined surfaces of the sleeve and compression member are drawn towards each other, and by the angle that at least one of the inclined surfaces makes with the pipe.
On pipe couplings manufactured for pipes of set dimensions, i.e. pipes manufactured to very close tolerances with little variation in O.D., the inclined surface(s) usually has a shallow taper or angle. When the axial load is applied by drawing two inclined surfaces together, which in most cases comprises tightening a nut and bolt connecting a pair of flanges extending radially outwardly from the inclined surfaces, either side of a gripping or sealing ring, the shallow taper helps to improve the gripping force.
However, when such a shallow angle is used on pipe couplers intended for use on a wide range of pipe diameters, a much greater range of axial movement may be required to produce the necessary radial inward movement of the gasket and, for example, the bolt length needed to impart pressure to and reduce the diameter of a sealing or gripping gasket by, e.g. 35 mm, is considerable.
To overcome this problem, the taper of the support surface can be steepened, but a drawback here is the initial requirement for a much greater force to be imparted by the bolt to create an efficient grip; moreover, the gripping force is not significantly further enhanced by the angle.
One known coupling device intended for use with a wide range of pipe O.D.s is disclosed in EP-A-0 794 378. In EP-A-0 794 378, there is disclosed a device comprising a sealing/gripping member which includes a substantially closed gripping ring comprising a plurality of slidably abutting elements and a pair of inclined support surfaces which can be moved axially towards each other, thereby pressing the elements radially inwardly against the pipe. The slidably abutting elements taper in a radial inwards direction and act in the manner of a camera iris when compressed. The radial contraction of the gripping ring is thus provided by virtue of the abutting elements sliding over one another and rotating such that the tapered inner edges of the elements become more radially aligned.
A development of the device shown of EP-A-0 794 378 is disclosed in EP-A-0 974 780. In EP-A-0 974 780, the gripping action is provided by a separate gripping ring held within a recess on the radially inner surface of the slidably abutting elements. The gripping ring, which would appear not to be axially moveable with respect to the slidably abutting elements, is described as being formed from spring steel and having gripping teeth pressed out of the plane of the ring.
Another known coupling device is disclosed in GB-A-2 227 067. This document discloses a coupling in which a gripping and sealing assembly comprises an annular sealing gasket, a metal force transmitting ring and a gripping ring. The gripping ring is formed from an array of circumferentially linked elements.
An object of the present invention is to provide an improved pipe coupling capable of being used with pipes having a wide range of ODs for a given nominal OD.
A further object of the invention is to provide a pipe coupling in which a firm gripping force can be applied to a pipe over a wide range of pipe ODs to prevent retraction of the pipe from the coupling under end loads.